Fixed Spree::Api::ProductsController#index to accept multiple ids

Fixes #3886
Relax money dependency
Bugfix: Taxons could not be ordered

If you reorder the taxons in the admin interface, it does not
have any effect, because the ordering of the taxons is not
used. Setting a default scope with this ordering fixes that.

Fixes #3891
Fixes #3833
Fixes #3390
Spree::Payment.class.undescore will always convert spree/payment

Fixes #3889
Fix fieldset not resizing on some @media sizes.

Fixes #3871
Fixes #3890
[api] Don't depend on ordering in taxons_controller_spec
Use correct default_scope syntax for Rails 4 in Taxon
Check for presence in Spree::CreditCard#expiry method

The expiry method needs to check for presence before parsing. An empty card expiration field will raise the error "no implicit conversion of nil into String" on submission.

Fixes #3847
Fixes #3896